[petsc-users] Question on DMPlexCreateFromCellList and DMPlexCreateFromFile

[Danyang Su]

Hi Matt,

I have a question on DMPlexCreateFromCellList and DMPlexCreateFromFile. 
When use DMPlexCreateFromFile with Gmsh file input, it works fine and 
each processor gets its own part. However, when use 
DMPlexCreateFromCellList, all the processors have the same global mesh. 
To my understand, I should put the global mesh as input, right? 
Otherwise, I should use DMPlexCreateFromCellListParallel instead if the 
input is local mesh.

Below is the test code I use, results from method 1 is wrong and that 
from method 2 is correct. Would you please help to check if I did 
anything wrong with DMPlexCreateFromCellList input?

!test with 4 processor, global num_cells = 8268, global num_nodes = 4250

!correct results

  check rank            2  istart         2034  iend         3116
  check rank            3  istart         2148  iend         3293
  check rank            1  istart         2044  iend         3133
  check rank            0  istart         2042  iend         3131

!wrong results

   check rank            0  istart         8268  iend        12518
   check rank            1  istart         8268  iend        12518
   check rank            2  istart         8268  iend        12518
   check rank            3  istart         8268  iend        12518


       !c *************    test part    *********************
       !c method 1: create DMPlex from cell list, same duplicated global 
meshes over all processors
       !c the input parameters num_cells, num_nodes, dmplex_cells, 
dmplex_verts are all global parameters (global mesh data)
       call DMPlexCreateFromCellList(Petsc_Comm_World,ndim,num_cells,   &
num_nodes,num_nodes_per_cell,      &
Petsc_True,dmplex_cells,ndim,      &
dmplex_verts,dmda_flow%da,ierr)
       CHKERRQ(ierr)


       !c method 2: create DMPlex from Gmsh file, for test purpose, this 
works fine, each processor gets its own part
       call DMPlexCreateFromFile(Petsc_Comm_World,                      &
prefix(:l_prfx)//'.msh',0,             &
                                 dmda_flow%da,ierr)
       CHKERRQ(ierr)

       !c *************end of test part*********************


       distributedMesh = PETSC_NULL_OBJECT

       !c distribute mesh over processes
       call DMPlexDistribute(dmda_flow%da,0,PETSC_NULL_OBJECT,          &
                             distributedMesh,ierr)
       CHKERRQ(ierr)

       !c destroy original global mesh after distribution
       if (distributedMesh /= PETSC_NULL_OBJECT) then
         call DMDestroy(dmda_flow%da,ierr)
         CHKERRQ(ierr)
         !c set the global mesh as distributed mesh
         dmda_flow%da = distributedMesh
       end if

       !c get coordinates
       call DMGetCoordinatesLocal(dmda_flow%da,gc,ierr)
       CHKERRQ(ierr)

       call DMGetCoordinateDM(dmda_flow%da,cda,ierr)
       CHKERRQ(ierr)

       call DMGetDefaultSection(cda,cs,ierr)
       CHKERRQ(ierr)

       call PetscSectionGetChart(cs,istart,iend,ierr)
       CHKERRQ(ierr)

#ifdef DEBUG
         if(info_debug > 0) then
           write(*,*) "check rank ",rank," istart ",istart," iend ",iend
         end if
#endif


Thanks and regards,

Danyang

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